A conventional lubricant for tractor-trailer couplings, rail-wheel systems and other heavy duty applications is grease. However, grease has serious limitations for operation and for environmental contamination. Following mating of the coupling components after an application of grease, a large portion of the grease is immediately lost due to difficulties of the grease adhering to the coupling or rail. The lost grease falls on parts of the vehicle piping and on the ground as a non-biodegradable contaminant. Further, grease dissipates during use causing its lubricating performance to deteriorate to potentially hazardous conditions. This known dissipation thereby encourages users to apply excessive amounts of grease to compensate. Moreover, exposed couplings, rails or wheels can become contaminated with dust and grit thereby forming a grinding compound which causes rapid wear to the bearing plates unless they are cleaned and regreased before use.
Typically, grease is reapplied every week or two. Its removal prior to regressing is accomplished with high pressure steam causing it to be flushed into the water supply. Alternatively, stronger solvents may be used to remove grease which are even more unacceptable from an environmental standpoint.
Lubricant compositions comprising, inter alia, solid lubricants and polymer media have been used as alternatives to grease and these lubricants have the advantage of forming a film on the metal surface, and accordingly, better adhesion. However, as the lubricant dissipates, the polymer medium may still contaminate the environment.
Aqueous lubricant compositions have been suggested but discarded as impractical in Swiss patent specification CH 669,207 A5, wherein a method of using an aqueous graphite dispersion for coating or painting sides of rails was discussed and discarded as the aqueous dispersion is apparently easily removed. The solution of CH 669,207 A5 is a composition which includes, inter alia, a polymer resin which has the same drawbacks as other polymer media as discussed above.
It is recognized in U.S. Pat. Nos. 5,173,204 and 5,308,516, that when the co-efficient of friction increases with speed, it is known as having a negative friction characteristic. The origin of much noise emission in steel rail-wheel transportation systems can be directly attributed to the fact the negative friction characteristic that under certain conditions arising in use, the wheels of such systems do not always roll over the rails but sometimes slide relative to them. This is most pronounced on curves. An effective way to eliminate the squeaking and chattering is by changing the friction characteristic from a negative one to a positive one. Hereinafter, the term "positive friction" means that the coefficient of friction increases with speed of sliding and a "high" coefficient of friction is greater than 0.10.
Apart from reduced friction (and noise) and wheel-rail wear, use of a friction modifier can prevent the initiation and growth of short pitch corrugation by preventing or eliminating the oscillatory motions, commonly known as roll-stick oscillations, which are excited in the rail/wheel interface by the presence of negative friction.
U.S. Pat. Nos. 5,173,204 and 5,308,516, teach that in a rail-wheel system, the lubricant composition should be applied to 25% all the wheels of a rail-wheel system. Considering that the effect is most pronounced on curves, a lot of lubricant, time and effort is required in order to ensure that there is sufficient lubricant.